Process of making lead carbonate.



UNlThD STATES PATENT FFICE.

GEORGE D. COLEMAN, OF BRIDGEWATER, MASSACHUSETTS;

PROCESS OF MAKING LEAD CARBONATE;

SPECIFICATION forming part of Letters Patent No. 649,507, dated May 15,1900.

Application filed February 10, 1899. Serial No- '705;145. (N0specimens.)

To (LZZ whom it may concern.-

Be it known that I, GEORGE D. COLEMAN, a citizen of the UnitedStates,residin g at Bridge water, in the county of Plymouth and State ofMassachusetts, have invented certain new and useful Improvements inProcesses of Making Lead Carbonate and I do hereby declare the followingto be a full, clear, and exact description of the invention, such aswill enable others skilled in the art to which it appertains to make anduse the same.

The present invention relates to an improvement in the art of makinglead carbonate, and more particularly to the art of making leadcarbonate from metallic lead.

All processes of making carbonate of lead known to me are more or lessobjectionable because of the fact that they are either tedious,expensive, or result in an impure product.

The objects of my invention are to improve the quality of the productand to produce a very pure carbonate of lead, to decrease its cost ofmanufacture, and to reduce to a minimum the time required in carryingout the process, as well as to secure better hygienic conditions in theworks.

To these ends, therefore, my invention consists in the art of makingcarbonate of lead hereinafter described, and more particularly set forthin the claims.

' In general my process consists in exposing metallic lead to the actionof a suitable oxidizing reagent, such as air, to corrode or oxidize it,then in exposing the product to the action of a suitable carbonatingreagent, such as carbonic acid, whereby the product of the oxidation islargely transformed into lead carbonate, and then exposing the productof the carbonating step to the action of a suitable oxidizing reagent,such as air, to transform the small quantities of metallic lead stillfound in the mass to the suboxids of lead, and at the same time totransform the small quantities of suboxid of lead thus formed andpresent in the mass at the beginning of the step to nascentleadprotoxid. Then the product of the last step is subjected to the actionof a suitable carbonating reagent, such as carbonic acid, therebyreducing the protoxid of lead to the carbonate, so that the product ofthis step is pure carbonate of lead.

While my process of making carbonate of lead is thus seen to consist inthe alternate exposure of the material, which at the beginning wasmetallic lead, to the action of oxidizing and carbonating reagentsalternately until all of the lead originally subjected to the action ofthe reagents employed is entirely transformed into carbonate of lead,the manner in which I carry out this process may vary in many respectswithout departing from the spirit of my invention. Still I prefer tocarry out this process in the following manneri First. Metallic lead,preferably comminuted by grinding or cutting into very small pieces, bywhich the action of the reagents thereupon, owing to the greater surfaceexposed, is materially facilitated, is subjected to the action of anoxidizing reagent, preferably pure air, containing no carbonic acid, andin order to remove protoxid of lead, which forms very rapidly upon thesurface of the metallic lead when so exposed, the whole mass is agitatedby stirring or tumbling, preferably in the presence of water, so thatthe lead shall be exposed to the oxidizing influence of the oxidizingreagent and then subjected to the washing action of the water, wherebythe newly-formed oxid will be washed off to present a clean surface tothe renewed action of the said reagent. Any suitable means may beemployed for this purposeas, for example, the apparatus for corrodinglead illustrated and described in Letters Patent granted me August16,1892, No. 481,004. This corroding or oxidizing step may be carried onat the ordinary temperature; but by preference the mass will bemaintained at a temperature of 127 Fahrenheit, as'I have found that thecorroding or oxidizing action is more rapid at or near this temperature.Of course I do not confine myself to this procise temperature, as goodresults can be obtained by usinglower or higher temperatures. Theproduct of this corroding or oxidizing operation will be abouteighty-five per cent. lead protoxid, eight per cent. lead hydrate, fiveper cent. lead suboxid, and two per cent. of unaffected finely-dividedmetallic lead, although under varying conditions it may departconsiderably from the proportions above given.

Second. The product of the first corroding or oxidizing step is nowsubjected to the action of a carbonating reagent, preferably carbonicacid. By preference the productof the corroding or oxidizing operationbefore being exposed to the carbonic acid will be cooled as much as isconveniently possible in order that the carbonating process may be morerapidly carried on, as I have found that carbonating progresses lessrapidly at higher than at lower temperatures. In orderto accelerate therate of carbonating the mass, I subject it to agitation by stirring ortumbling, as in oxidizing.

' This carbonating operation is continued until the product of thecorroding or oxidizing step has been almost entirely transformed intoalead carbonate,th.e resulting mass being approximately ninety-sixpercent. lead carbonate, two per cent. suboxid of lead, and two percent. unafiected metallic lead, as before, although under varyingconditions it may depart considerably from these proportions. It will beobserved that by this operation the protoxid of lead and the hydrate oflead have been transformed into lead carbonate and that some of thesuboxid of lead has taken up oxygen mixed with the carbonic acid orwater, becoming protoxid of lead, so that when this operation iscompleted there still remains present about two fifths the quantity ofsuboxid of lead present at the beginning of the operation. WVhatevermetallic lead was present is of course chemically unaifected by thisstep, although the attrition incident to the step will result in itsbeing more finely divided than before.

Third. The product is now transformed to another vessel and subjected tothe action of an oxidizing reagent, preferably air, the wholemass beingproperly heated to a temperature of 125 Fahrenheit, although itmay varywithin considerable li'mits without de- I analysis or by the change ofcolor of the mass from white with a tinge of blue, due to the presenceof finely-divided metallic lead, to white with a tinge of yellow, due tothe presence of lead protoxid. The composition of the mass at the end ofthis operation will be ninety-six per cent. lead carbonate and four percent. lead protoxid, although under varying conditions it may departconsiderably from these proportions, thus leaving the carbonateunaffected by this operation, but

' entirely removing all traces of metallic lead and suboxid of lead fromthe mass.

I have found that the light tinge of blue which is referred to in thespecification of the patent to Gardner of August 28, 1840, No. 1,744, isdue to'the presence of metallic lead or suboxid of lead, or both, andwhile that specification states that this light tinge of blue disappearsin the process of drying I have found that it only disappears from thesurface of the mass by reason of the oxidation of the surface metalliclead by the air and the subsequent transformation of the suboxid of leadthus produced or originally present in the mass into carbonate by takingup carbonic acid from the air, and thus preventing the recognition ofthe presence of metallic lead or suboxid of lead by the eye. Still itdoes not remove it from the body of the mass, and it is for the verypurpose of removing this very finely-divided lead or suboxid of lead, orboth, indicated by this light tinge of blue, that at this stage in myprocess of making lead carbonate I subject it to this further oxidizingprocess in order to completely remove metallic lead or suboxid of lead,or both, from the mass. In this important respect my invention is verysharply distinguished from the patent to Gardner above referred to,which results, for the reasons stated, in a product containing metalliclead or suboxid of lead, or both, and while this is not the onlyimportant distinction between my process and that of Gardner it is onethat it is pertinent here to advert to, reserving for a more appropriateplace another distinction hereinafter to be pointed out.

Fourth. The product is now subjected to the action of a carbonatingreagent, preferably carbonic acid. While this may be done by simplycutting off the supply of air and introducing the carbonating reagentinto the vessel containing the mass, I prefer first to cool the entiremass by pumping it out of the vessel and passing it through suitablecooling pipes or vessels to reduce the tempera= ture to the normaltemperature of the air or still further, if convenient. It will beunder-- stood that the operation of carbonating, as

reagent into the bottom of the vessel, so as I to percolate up throughthe mass to thereby bring the reagent into intimate contact with allportions of the same. This operation is continued until all of the leadprotoxid is transformed into lead carbonate, thus producing a mass whichconsists entirely of lead carbonate and water.

It is to be observed that in the specification of the patent abovereferred to it is proposed to make white lead byintroducing carbonicacid in conjunction with a portion of atmospheric air into a vesselcontaining granu lated metallic lead, while by my process the oxidizingreagent and the carbon ating reagent are introduced alternately into thevessel containing the lead to be treated. I have found that theoperation is very much more satisfactorily and economically carried outif these operations are made successive and not coincident besideswhich, by heating the mass during the oxidizing operations and by cooling it during the carbonating operations, I am able to secure betterworking conditions than if the two operations were carried on at thesame time. So, while I may or may not use heat during the oxidizingoperations, my process is clearly distinguished from the said Gardnerpatent by reason of introducing the reagents separatelyinto the vesselcontaining the material to be operated upon. This is the secondimportant difference between my process and the process described in theabovenamed patent.

Having thus described my invention, I claim as new and desire to secureby Letters Patent of the United States- 1. The art of making pure leadcarbonate which consists in subjecting metallic lead and the successiveproducts therefrom to the separate, successive and repeated actions ofan oxidizing reagent and a carbonating reagent, such actions beingrepeated until all the metallic lead has been converted into leadcarbonate, substantially as described.

2. The art of making pure lead carbonate which consists in subjectingmetallic lead and the successive products therefrom to the separate,successive and repeated actions of an oxidizing reagent and acarbonating reagent and heating the mass during the oxidizing operationsand cooling it during the carbonating operations, such actions beingrepeated until all the metallic lead has been converted into leadcarbonate, substantially as de scribed.

3. The art of making pure lead carbonate which consists in subjectingmetallic lead in the presence of water to the oxidizing action ofatmospheric air at a temperature of approximately 125 Fahrenheit, insubjecting the product of the last-named step to the action of carbonicacid at a lower temperature, in subjecting the product of the last-namedstep to the oxidizing action of atmospheric air at a temperature ofapproximately 125 Fahrenheit, and in subjecting the product of thelast-named step to the action of carbonic acid at a lower temperature,whereby all the metallic lead is converted into lead carbonate,substantially as described.

In testimony whereof I affix my signature in presence of two witnesses.

GEORGE D. COLEMAN.

Vituesses:

T. HART ANDERSON, JAMEs V. Ron.

